This invention relates to ethyleneurea-glutaraldehyde resins, urea-ethyleneurea-glutaraldehyde resins, their synthesis, as well as their application as adhesives for bonding lignocellulosic material such as for the manufacture of particleboard, plywood, hardboard, fiberboard, waferboard, oriented strandboard, and the like.
One of the major applications of urea-formaldehyde resins is as a binder for lignocellulosic material. Urea-formaldehyde resin is cheap and easy to use. It is colorless. Fast cure is also an advantage. Its chemical structure shows hydrolyzable methylene-ether linkages and methylol functions, which create the potential for giving off formaldehyde vapor after curing. Indeed, one of the disadvantages associated with urea-formaldehyde resin-bonded particleboard is that it slowly emits formaldehyde fumes. Due to environmental, health, and regulatory issues related to formaldehyde emissions from wood composite products, development of new adhesive systems which do not contain formaldehyde is of great interest.
Various compositions and methods have been developed to avoid formaldehyde release from adhesives in the manufacture of lignocellulosic panels. The Shiau et al U.S. Pat. No. 4,536,245 of Aug. 20, 1985 discloses urea-formaldehyde resins modified with melamine for use as a binder for such panels. The Salzburg et al U.S. Pat. No. 4,395,504 of July 23, 1983 shows a formaldehyde-free adhesive system for the manufacture of particleboard by the reaction product of a cyclic urea, e.g., ethyleneurea, and glyoxal. The instant invention shows advantageous properties over the use of an ethyleneurea-glyoxal resin. The instant invention uses an ethyleneurea-glutaraldehyde resin or a urea-ethyleneurea-glutaraldehyde resin to avoid the formaldehyde fumes. Other references are of less interest than the Salzburg et al patent. Thus, the Fisher et al U.S. Pat. No. 4,906,727 of Mar. 6, 1990 discloses a binder obtained by the reaction of urea or certain alkylene ureas with certain aldehydes. The Cummings patent, U.S. Pat. No. 4,906,726 of Mar. 6, 1990, discloses surface coatings prepared from complex mixtures which include the reaction product of polyaldehydes such as glyoxal or glutaraldehyde or derivatives thereof with urea. The Petersen et al U.S. Pat. No. 4,202,751 of Sept. 2, 1980 discloses resins prepared from urea and certain monoaldehydes which are disclosed as surface coating binders. The publication of European patent application 37,706 of Oct. 14, 1981 discloses a resin made from an ethyleneurea and formaldehyde for use as a flame retardant additive when in admixture with an ammonium phosphate.